An oil supply device which is assigned to a wheel is disclosed in the following patent document 1 (PTL1). This oil supply device is configured so as to supply oil to a hub bearing which rotatably supports a hub connected with a disk wheel of a wheel. According to this configuration, oil serves as a lubricant in the hub bearing. Moreover, in such a configuration, in order to seal the oil supplied to the hub bearing, it is common to use a well-known oil seal. This oil seal achieves a function for sealing the oil supplied to the hub bearing with a seal lip slidingly contacting a sliding surface of the hub bearing.